We are investigating the role of calcium on the biosynthsis of proparathyroid hormone and parathyroid hormone in the parathyroid gland of several animal species. Current studies include chemical characterization of proparathyroid hormone sites and mechanism of conversion to prathyroid hormone and the packaging and secretion of the latter. We also are investigating adapt!tion of the parathyroid gland to calcium stress in terms of synthesis of the hormone and prohormone.